<template>

        <ul class="list">
            <li class="item" v-for="item in letters" :key="item"
                    :ref="item"
                  @touchstart.prevent="handleTouchStart"
                    @touchmove="handleTouchMove"
                    @touchend="handleTouchEnd"
            @click="handelClick">{{item}}</li>
        </ul>

</template>
<script>
export default {
    name: "CityAlphabet",
    props: {
        cities: Object
    },
    computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
    methods: {
        handelClick(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
    }
}
</script>
<style lang="stylus" scoped>
@import '~styles/variables.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
